Why does this ruby case statement give an unexpected result?

Why does the following ruby code return "" instead of "Code is empty"?

code = ""
case code
when code.empty?
  "Code is empty"
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  code
end

Because your code is comparing code to code.empty?, i.e., the result of code == code.empty?, which is false. A string can degrade to a boolean, but the explicit equality of '' == true will evaluate to false.

The expression code.empty? is a method call that calls the method empty? which returns the value true. The true value is then compared to the code variable using the expression true === code, which is false, so it executes the else block of code.

This is probably what you want instead:

case code
when ""
  "Code is empty"
else
  code
end

A simpler way to do it is by using the ternary operator:

code.empty? ? "Code is empty" : code